1. Field of the Invention
The present invention relates to a solid state image pickup apparatus, and more particularly, to a technique to expand the dynamic range thereof.
2. Description of the Related Art
In an amplification-type image pickup apparatus such as that known as a CMOS image sensor, there are various known electronic shutter techniques to control starting and ending of accumulation for all pixels over an entire plane without using a method of mechanically blocking light.
In a technique associated with an electronic shutter disclosed in Japanese Patent Laid-Open No. 2006-246450, a charge generated in a photoelectric conversion part in a signal charge generation period is transferred to a charge storage part, and, after the end of exposure, the photoelectric conversion part is reset to remove the charge remaining in the photoelectric conversion part thereby achieving a function of the electronic shutter.
This technique is characterized in that functions are implemented separately by dedicated parts such that the photoelectric conversion part basically performs only photoelectric conversion and charge accumulation during an exposure period is performed by the charge storage part disposed adjacent to the photoelectric conversion part. Note that the charge storage part is disposed separately from the FD region. Because the saturation number of charges in the photoelectric conversion part is small, transferring of the charge from the photoelectric conversion part to the charge storage part can be performed using a low voltage. This device can be easily produced by a simple process based on a general CMOS production process, i.e., the production thereof is easier than CCD or other similar devices. Note that herein and elsewhere in the present description, it is assumed that charges are provided by electrons. Thus the expression “the number of charges” should be read as “the number of electrons” in the case where electrons are used.
In the technique disclosed in Japanese Patent Laid-Open No. 2006-246450, the provision of the charge storage part in each pixel leads to an increase in the saturation amount of charge. However, the increase in the saturation amount of charge can cause a signal to be limited in terms of a range by the dynamic range of a reading circuit disposed at a stage following the photoelectric conversion part and the charge storage part. This situation arises from the above-described configuration in which the function of photoelectric conversion and the function of accumulating the signal charges are separately implemented, and each of these two functions is individually optimized.
In view of the above, the present invention provides a technique to produce an image signal by fully using the signal charges, whose amount is increased by the charge storage part disposed separately, without being limited by the dynamic range of the reading circuit disposed at the following stage.